The (current) future of human spaceflight: the Space Launch System

NASA just announced its new program for human spaceflight: the Space Launch …

In the wake of the end of the Space Shuttle program, and the effective cancellation of the Constellation program, Americans (and the rest of the world) have been wondering what comes next. On Wednesday, NASA announced the Space Launch System (SLS), a new heavy-lift launch vehicle that will carry astronauts and cargo to low-Earth orbit (LEO), initially, and eventually beyond. This new vehicle, planned for a 2017 launch at the earliest, uses some components from previous designs (for instance, the engines from the Shuttle program and the Orion crew vehicle from Constellation) but is a new design, and it will be the most powerful rocket yet built. Let’s go over some of the (announced) details, and see what exactly NASA has come up with.

First: the hardware. NASA focused on a design that would be both modular, combining different components for different missions, and reuse existing designs. The main engines will all be liquid-fueled, using hydrogen and oxygen (like the Space Shuttle main engine). To avoid the unnecessary expense of entirely new engines (see the Ares rockets), the new vehicle will use the RS-25 engines from the Space Shuttle main engines for the core stage and the J-2X, a variant of the J-2 engine from the Apollo-era Saturn V rockets, for the upper stage. The J-2X was originally designed for the Constellation program as a cheaper and more efficient engine compared to those used in the Space Shuttle.

The initial (announced) design will have a payload capacity of 70 metric tons (154,000 pounds), with a fully fueled liftoff weight of 5.5 million pounds (about 2500 metric tons), and use three RS-25 engines for a single stage, with solid rocket boosters similar to those used on the Shuttle. With additional boosters, this design could support 100 metric tons. Later, by adding two more RS-25 engines and an upper stage J-2X engine, the payload capacity will be upgraded to 130 metric tons (268,000 pounds). For some perspective, the three-stage Saturn V rocket used in the Apollo missions (the most powerful ever used, and hasn’t been used since 1973) has a maximum payload capacity of 119 metric tons.

For those unfamiliar with the concept of rocket staging, here’s a quick explanation. Chemical rockets basically generate thrust by expelling mass; in fact, the propellant mass is typically much larger than the actual payload and structure of the vehicle (for instance, propellant makes up 80 percent of the mass of the fully fueled Space Shuttle system at launch). In order to avoid carrying up unnecessary structural mass (which in turn requires additional propellant, and so on), rocket designers employ staging, where the entire vehicle is broken into self-contained stages that disconnect when their propellant is exhausted—think of the boosters and external tank falling off once the Shuttle gets to a certain altitude. Multiple stages increases complexity, but this is considered a worthy tradeoff when compared against considerable added propellant.

Now, where exactly is this vehicle going to take us? This part is a little more ambiguous. NASA plans on using the six-person Orion crew vehicle, now known as the Multi-Purpose Crew Vehicle (MPCV), with the SLS. The initial design could carry astronauts and cargo to LEO, where the International Space Station (ISS) and most satellite are located—but NASA is planning on using commercial spaceflight companies like SpaceX and Orbital Sciences to resupply the ISS, and their vehicles will be ready sooner than the SLS.

That leaves near-Earth asteroids, cis-lunar space, the Moon, and beyond (think Mars) for the SLS. I’m sure we’ll hear more about the destinations as the initial launch date (2017) approaches, but it is exciting to see that NASA has come up with a solid design, especially one that reuses known elements. The modularity of the design also allows for different missions, just by adding more boosters and an upper stage. Hopefully this pragmatism will allow this program to avoid the sweeping budget cuts of the current US government.

104 Reader Comments

This is a terrible waste of money and a giant step backwards. WE need heavy lift capability but with this approach you would be better off just getting the Saturn V up and running again. Far less money would be wasted and NASA could focus on new technology to replace the space shuttle with.

Unfortunately if Obama loses the 2012 election, the date slips significantly beyond 2017, or congress crushes the program by failing to provide enough funding to meet milestones; it will end up along side every other shuttle replacement in the graveyard of cancelled NASA programs.

You do realize that it was Obama who pulled the plug on the shuttle program in the first place? And who wants to cut from NASA quite badly?

I'm not saying they'd be in any better shape with some of these Republican nominees (not that they're really a danger to Obama's presidency - they're lackluster at best) but I still haven't forgiven him for that whole "let's have private industry handle space" thing. In fact, that, along with the continued survival or the Patriot Act, are the two things I am most angry at him for. Yes, I'm aware that I'm a complete nerd.

7.8km/s is the orbital velocity, but that's only half the equation. You still have to get 200km up.

(2*9.81*h)^.5+v

That's not correct. That would be the velocity if you launched vertically, coasted to 200 km, then applied the 7.8 km/s horizontally. Real launch vehicles don't work that way. In reality you do a gravity turn into a an orbit that has a 200 km apogee then make a small circularization burn. The velocity required is closer to the vector addition of the two components:

@SinclairZX81: you'd owe me several keyboards, if I wasn't still grinning from ear to ear as well!

If I wake myself up giggling in the middle of the night, I'll know who to blame. <high five!>

Heh. Thanks, and sorry about any keyboard damage. :-)

You pretty much have to wrap this stuff in humor, it's so tragic. All of the things I wrote were from the open media and I just went back and fixed a factual error where I had Obama announcing the Orion reinstatement in the VAB - he actually announced the "New Plan" there prior to the Orion reinstatement.

I wish I could be less cynical about our prospects for actually getting a beyond-LEO program into actual hardware and flight before I die, but the prospects continue to dim with each "We're going in about 15-20 years!" statement that comes, about five to ten years apart, from successive administrations.

The Space Frontier Foundation attacks this system intensly, headlining an article "Monster Rocket Will Eat American Space Program." Other sources say the Obama administration is already trying to kill the program. Personally I was excited by the design decisions but some in the private sector see the funding to develop the SLS as competition for their pending and future contracts and are attacking it like the Right attackes taxes. The entire article is so vehement as to destroy its credibility.

I haven't read the article referenced but there is no doubt in my mind this project will distroy NASA. It is a waste of money to build a rocket that basically duplicates the Saturn V. It is even more questionable to build such a platform without clear plans for it's use. (Finding uses is easy, convincing congress is harder). Beyond that return to earth in a capsule is so 1900's.

Unfortunately if Obama loses the 2012 election, the date slips significantly beyond 2017, or congress crushes the program by failing to provide enough funding to meet milestones; it will end up along side every other shuttle replacement in the graveyard of cancelled NASA programs.

You do realize that it was Obama who pulled the plug on the shuttle program in the first place? And who wants to cut from NASA quite badly?

No, Bush (Jr.) cut the shuttle program. Obama killed Bush's replacement - Constellation - leaving us effectively with no manned vehicle program at all. The reinstatement of Orion was (and is) a jobs-progam payoff to Senator Nelson from Florida and a couple of others O-man needed to help push through the Healthcare deal, and SLS is caught between the White House, who doesn't want it, and Congress, who does. We only got the announcement of the SLS reference design this week because Congress issued subpoenas to NASA leadership after they slow-boated the project for nearly twenty-one months, trying to stay out of the line of fire from both sides. It was originally due last January. See my massively-long timeline of the whole fiasco on page two of this thread.

I'm *all* for criticism of the past two administration's handling of space policy, but let's keep the particular blame items on the proper targets.

People keep saying "THIS JUST DUPLICATES SATURN V!" Well, that's not so bad. Tell me you're not seriously suggesting we just dust them off and use them instead? The existing structures we have left were made into museum pieces, the machinery to make them is gone, the brain trusts that banged them up are no longer viable. We still have the bluprints on microfilm, but it would probably be at least as expensive to try and rebuild the production lines to get duplicate rockets rolling compared to gearing up to make a new rocket. We also have a few places where the intervening march of technology has made things more capable than what was available 40 years ago.

You are correct in that I didn't consider losses, 7.8km/s is the 'exact' delta-V required for ~200km LEO.

7.8km/s is the orbital velocity, but that's only half the equation. You still have to get 200km up.

(2*9.81*h)^.5+v

You're talking about gravity losses. In looking back at my notes I see they're quite a bit higher than I remember, around 1-1.5 km/s. So we're nearly there with gravity and drag losses, and rotational benefits. Here's the delta-V budget breakdown of the Saturn V according to my notes:

People keep saying "THIS JUST DUPLICATES SATURN V!" Well, that's not so bad. Tell me you're not seriously suggesting we just dust them off and use them instead? The existing structures we have left were made into museum pieces, the machinery to make them is gone, the brain trusts that banged them up are no longer viable. We still have the bluprints on microfilm, but it would probably be at least as expensive to try and rebuild the production lines to get duplicate rockets rolling compared to gearing up to make a new rocket. We also have a few places where the intervening march of technology has made things more capable than what was available 40 years ago.

My understanding is that there's also quite a bit of small hardware that was designed into Saturn and is no longer available as exact replacement parts. So there are a lot of reasons for not wanting to rebuild Saturns exactly from the old prints.

A well written piece if you ask me. Sadly we (America) are in need of some leadership with a bit of intelligence and a desire to actually move things forward. There is no rational reason to go backwards with projects that will cost billions to build a modern version of an exist capability. We can use that existing tech while striving to develop modern capabilities.

People keep saying "THIS JUST DUPLICATES SATURN V!" Well, that's not so bad. Tell me you're not seriously suggesting we just dust them off and use them instead? The existing structures we have left were made into museum pieces, the machinery to make them is gone, the brain trusts that banged them up are no longer viable. We still have the bluprints on microfilm, but it would probably be at least as expensive to try and rebuild the production lines to get duplicate rockets rolling compared to gearing up to make a new rocket. We also have a few places where the intervening march of technology has made things more capable than what was available 40 years ago.

My understanding is that there's also quite a bit of small hardware that was designed into Saturn and is no longer available as exact replacement parts. So there are a lot of reasons for not wanting to rebuild Saturns exactly from the old prints.

Yes, DriverGuru, you're correct. There are a lot of small parts that go into rockets (valves, for instance) that are made by fairly small companies. Many of these companies have gone out of business since then, or have otherwise moved onto other things.

Without those parts you can't just rebuild the rocket. You'd have to redesign it to be built in the modern era.

Because the SLS will re-use old Space Shuttle RS-25 main engines, these engines have already been removed from the Space Shuttle orbiters. For example, before Discovery is delivered for permanent display at the Smithsonian Air and Space Museum at Dulles Airport next April, the orbiter will be fitted with fake exhaust nozzles and covers to fill in the holes. This would be akin to the Smithsonian displaying the Enola Gay B-29 bomber that dropped the first A-bomb without any radial piston engines, just empty cowlings.

The Shuttle orbiters Discovery, Atlantis, and Endeavour are valuable historical artifacts that are being gutted in order to scavenge parts for an SLS that may never fly. Is the US so broke that we have to fly used engines in the SLS?

To add insult to injury, after launch each SLS stage containing original RS-25 Shuttle engines will end up in the bottom of the ocean.

Because the SLS will re-use old Space Shuttle RS-25 main engines, these engines have already been removed from the Space Shuttle orbiters. For example, before Discovery is delivered for permanent display at the Smithsonian Air and Space Museum at Dulles Airport next April, the orbiter will be fitted with fake exhaust nozzles and covers to fill in the holes. This would be akin to the Smithsonian displaying the Enola Gay B-29 bomber that dropped the first A-bomb without any radial piston engines, just empty cowlings.

The Shuttle orbiters Discovery, Atlantis, and Endeavour are valuable historical artifacts that are being gutted in order to scavenge parts for an SLS that may never fly. Is the US so broke that we have to fly used engines in the SLS?

To add insult to injury, after launch each SLS stage containing original RS-25 Shuttle engines will end up in the bottom of the ocean.

Like I said before, it's even more than that:

Quote:

NASA’s three retired Space Shuttle orbiters are set to donate their entire Main Propulsion Systems (MPS) to the opening salvo of Space Launch System (SLS) Heavy Lift Launch Vehicles (HLV). The work to remove the MPS’ array of plumbing, tanks and valves from the aft of the orbiters would result in a delay of six to nine months to the scheduled arrival at their museums.

This effectively relates to the guts of the orbiters, specifically known as the Orbiter MPS.

The Orbiter MPS includes major hardware items such as the Propellant Management System (PMS).

The MPS PMS consists of manifolds, distribution lines, and valves that transport propellants from the tanks to the three main engines for combustion, and gases from the engines to the tank for pressurization.

The PMS is the lifeline of the integrated MPS. In addition to its primary function of feeding propellants from the External Tank to the engines during powered flight, the PMS also controls the loading of propellants before launch, the post-MECO propellant dump and vacuum inerting.

I think I read somewhere that the Falcon Heavy would be an even better alternative to SLS. Cheaper & with a higher payload capacity.

Can someone confirm?

Cheaper sure, but max payload capacity on Falcon Heavy is somewhere around 50 tons if I recall correctly. Also in SpaceX's press release about the Falcon Heavy, they mentioned that it is not designed to compete with SLS and they fully support NASA developing a heavy lift booster on their own.

Oddly not a word about SpaceX doing the same thing in 3 years 140 tons LEO with the Falcon X at a fraction the cost.

I love what SpaceX are doing and I looking forward to watching their space programme develop. With that said, I sincerely doubt they'll be launching Falcon Xs three years from now. I hope they'll have a steady schedule of F9, F9H launches going and it wouldn't surprise me at all if they're test firing the Merlin 2 engine by then. Complete Falcon Xs though - even allowing for the modularity of their rocket designs - seems like a stretch too far.

Although I'll happily send Sethdayal a bottle of champagne on the third anniversary of this post if I'm wrong

Don't misunderstand me, I am a *massive* proponent of Space X over the assraping we have gotten from ULA. And for some things, like GPS satellites where losing 1 isn't the end of the mission, it's a fantastic way to go.

But for HSF, no, I'd go with something that has as close to 100% reliability as is feasible. It makes it easier to get candidates to fly.

It's certainly a bit too early to make that decision one way or the other. But if it's my ass riding on top, I'd prefer the rocket that wasn't designed to use solid boosters just to keep some senators happy.

if the mission required assembly of something like Hubble, you'd have to put astronauts in orbit to do the work, and that would not be cheaper than launching a single larger vehicle.

Maybe I'm taking your comment too literally, but both Hubble and JWST are well within the launch capabilities of the Falcon Heavy and Falcon 9, respectively. I'm too lazy to do the math right now, but you might even get away with launching both on a single Falcon Heavy.

The only foreseeable payloads which exceed the limits of those launchers would be space stations, or lunar/interplanetary missions. In either case, in-orbit assembly is something which would need to occur regardless of the number of launchers. Performing an in-orbit rendezvous can even be fully automated, so if more than 2 launchers are required it would be possible for the crew to go up last once everything else is in one place.

The Apollo missions, for example, could be split by launching the Lunar Excursion and Command modules separately and making a rendezvous in orbit. This would require almost no change to the mission or equipment, as the stack had to be launched upside-down. To be fair, though, there aren't any launchers today, or near future, which would be capable of doing that with two launches. They would all require a third launch to deliver an upper stage to push everything to TLI. Then again, that would still be a significant cost savings over Saturn V, the Space Shuttle or (based on any reasonable estimate) the SLS.

While refinements to conventional design are always welcome, this is quite disappointing. More so, when you consider that the aerospike engines from the cancelled X-33 project were completed and tested successfully.

Because the SLS will re-use old Space Shuttle RS-25 main engines, these engines have already been removed from the Space Shuttle orbiters. For example, before Discovery is delivered for permanent display at the Smithsonian Air and Space Museum at Dulles Airport next April, the orbiter will be fitted with fake exhaust nozzles and covers to fill in the holes. This would be akin to the Smithsonian displaying the Enola Gay B-29 bomber that dropped the first A-bomb without any radial piston engines, just empty cowlings.

I have to point out that in the original Enola Gay exhibition, they didn't have the entire bomber, just pieces. And in the current exhibit they do have an entire B29, but it's far from original equipment; considerable "restoration" work has been done. (See http://nasm.si.edu/exhibitions/gal103/enolagay/ )

Quote:

The Shuttle orbiters Discovery, Atlantis, and Endeavour are valuable historical artifacts that are being gutted in order to scavenge parts for an SLS that may never fly. Is the US so broke that we have to fly used engines in the SLS?

To add insult to injury, after launch each SLS stage containing original RS-25 Shuttle engines will end up in the bottom of the ocean.

Well... we do have some confidence that they'll work.

But Jerry Pournelle (article linked above) raises the point that those engines are more complicated and heavier than they need to be, because they're designed to be reusable. Why take a reusable design and use it as a throwaway?

Maybe I'm taking your comment too literally, but both Hubble and JWST are well within the launch capabilities of the Falcon Heavy and Falcon 9, respectively. I'm too lazy to do the math right now, but you might even get away with launching both on a single Falcon Heavy.

Yup, piece of cake, with plenty of room to spare. The stated payload to LEO of the Falcon Heavy is 53 tons. Hubble's mass is 11 tons and JWST will be about 6 tons. (Yes, that's right, JWST has half the mass of Hubble despite having a mirror almost 6 times larger in area.). So there's 17 out of your 53 tons on the Falcon Heavy. :-) Even adding in a factor of 2.5 (ish) mass penalty for trajectories out to L2 instead of LEO, you've still got tons of mass leftover, literally. The Falcon Heavy is a big, big bird.

But Jerry Pournelle (article linked above) raises the point that those engines are more complicated and heavier than they need to be, because they're designed to be reusable. Why take a reusable design and use it as a throwaway?

They planned to use them because they are existing assets, paid for and tested and well understood. Thus it allows them to work on an expendable version while using a known good engine for the first few flights. It will most likely take years to build the expendable version of the engine given the miniscule funding they'll have to dedicate to it being built. The SSME is significantly more efficient than the RS-68 is or will be and the RS-68 would need to be redesigned from an ablative nozzel to a regen nozzle as clustering them so close together would likely lead the nozzles to fail otherwise. The SSME's don't last forever, so why not use them, rather then let them rot in a museum? There are older SSME's that are no longer useable if you really need to see a real one. One of them is hanging on display at KSC.

It takes some of the risk out of the first few flights by allowing you to fly systems you know work as you work out the kinks in other areas that are brand new. While I'm not a fan of SLS, I can see the reasoning to use those engines. No other program will need them and its not like we will suddenly decide to fly the orbiters again. That will happen around the same time we fly one of the Saturn V's on display.

But Jerry Pournelle (article linked above) raises the point that those engines are more complicated and heavier than they need to be, because they're designed to be reusable. Why take a reusable design and use it as a throwaway?

They planned to use them because they are existing assets, paid for and tested and well understood. Thus it allows them to work on an expendable version while using a known good engine for the first few flights. It will most likely take years to build the expendable version of the engine given the miniscule funding they'll have to dedicate to it being built. The SSME is significantly more efficient than the RS-68 is or will be and the RS-68 would need to be redesigned from an ablative nozzel to a regen nozzle as clustering them so close together would likely lead the nozzles to fail otherwise. The SSME's don't last forever, so why not use them, rather then let them rot in a museum? There are older SSME's that are no longer useable if you really need to see a real one. One of them is hanging on display at KSC.

It takes some of the risk out of the first few flights by allowing you to fly systems you know work as you work out the kinks in other areas that are brand new. While I'm not a fan of SLS, I can see the reasoning to use those engines. No other program will need them and its not like we will suddenly decide to fly the orbiters again. That will happen around the same time we fly one of the Saturn V's on display.

The problem with the RS-68 needing a regenerative nozzle is more to do with the fires of Hell SRB exhaust. But either way, there have long been plans for a lighter, cheaper, throwaway RS-25. In its current iteration, it’s called the RS-25e, and it will be switched to after we run out of old RS-25d engines.

Actually, though, I only skimmed Pournelle’s post, but it looks like he was referring to the SRBs. In which case it should be mentioned that there is a planned competition for the boosters after the initial flights – the core will be designed with fairly neutral attach points. They may even turn into liquid boosters.

Kyle Niemeyer / Kyle is a science writer for Ars Technica. He is a postdoctoral scholar at Oregon State University and has a Ph.D. in mechanical engineering from Case Western Reserve University. Kyle's research focuses on combustion modeling.